1. Technical Field
This invention relates generally to vacuum deposition and etching apparatus, and more particularly to a plasma source utilizing coupled ECR microwave and radio-frequency (RF) plasmas; the apparatus particularly employing line cusp magnetic multipole structures in both plasma regions for enhancing plasma confinement and producing a uniform plasma over a large substrate area, and also incorporating an electrically-biased magnetic filter for controlling the properties of the ECR microwave and RF plasmas.
2. Prior Art
In U. S. Pat. No. 5,032,202, one of the inventors provided an improved ECR microwave plasma source featuring a magnetic multipole construction for both the plasma confinement and plasma generation, and which also provides a uniform plasma for large area plasma processing. Like ECR microwave plasma sources before it, the plasma source relies solely on microwave energy to produce its plasma. In microwave plasma sources, variations of the plasma uniformity are a sensitive function of gas pressure and magnetic field in the microwave launcher.
Parallel plate radio-frequency (RF) reactors are another type of vacuum deposition and etching apparatus. See, for example, C. M. Melliar-Smith and C. J. Mogab, "Plasma-Assisted Etching Techniques for Pattern Delineation", in Thin Film Processes (J. L. Vossen and W. Kern, Eds.), Academic Press, New York, Chapt. V-2 (1978) pp.497-556. It is well known with parallel plate radio-frequency (RF) reactors that it is difficult to produce desired high density and uniform plasma at low pressures below 1 mtorr. Low pressures are desired to minimize gas scattering because the uniformity and directionality become more important as the sub-features are reduced in size for manufacturing of the electronics.
Recently, the use of electron cyclotron resonance (ECR) modes and static magnetic field structures have been reported in connection with parallel plate RF reactors (U. S. Pat. Nos. 4,585,668; 4,630,566; 4,691,662; 4,727,293; 4,906,900; and 5,081,398).
In one of these pats. 4,691,662, Roppel et al feeds charged excited species to the active RF plasma from a physically separated ECR microwave disk plasma. Roppel characterizes his active plasma as a microwave and RF plasma (or hybrid plasma) since it includes species from both microwave excitation and RF excitation. Roppel was able to achieve flexibility by controlling reactive species of the hybrid plasma. However, the operating pressure range was not reported The plasma source appears to operate at pressures well above 1 mtorr because of limited magnetic confinement for both the disk microwave plasma and the hybrid plasma. In fact, FIG. 1 of the 4,691,662 patent depicts some of the magnets 20 located on the sliding plate of the microwave cavity. In the Roppel apparatus, a resonant cavity is used to induce strong microwave electric fields which in turn create the microwave driven plasma inside a quartz dish. In such a source, the frequency required of the power supply decreases inversely proportional to the cross-sectional area of the microwave plasma. Consequently, it is difficult in such a source to create a uniform plasma over a large article at low pressures below 0.1 mtorr as needed for manufacturing microelectronics.